Biopropionic acid production via molybdenum-catalyzed deoxygenation of lactic acid

Abstract

As the search for non-fossil based building blocks for the chemical industry increases, new methods for the deoxygenation of biomass-derived substrates are required. Here we present the deoxygenation of lactic acid to propionic acid, using a catalyst based on the non-noble and abundant metal molybdenum under relatively mild reactive distillation conditions (200–270 °C). Good yields of sodium propionate (up to 41%) can be obtained with either triethylene glycol dimethyl ether or water as the solvent in the presence of one equivalent of sodium hydroxide, without an external reductant, and using an industrially relevant feedstock of 44% lactic acid in water. Mechanistic studies show that several reactions occur simultaneously, including decarboxylation and decarbonylation of lactic acid, dehydration, and deoxygenation. The major pathway of propionic acid formation was determined with isotopic labeling studies to proceed via direct C–O cleavage, and to a lesser extent via the dehydration/hydrogenation pathway involving acrylic acid.